What a great offer from Eric, he should have "some" insight on, well, what-do-you-know - forum advertising.
I would of course also look into juicyads, either for thei filler ads which will rotate the whole time or for direct sales. If it's in mainstream, why not give Google Adsense a try? Also there's Black Label Ads/Adbrite (Adult/Mainstream) which you could also give a shot and see which ones are best for you.